/Engine/Plugins/Online/OnlineSubsystem/Source/Public/Interfaces/OnlineExternalUIInterface.h
Displays the UI that prompts the user for their login credentials. Each platform handles the authentication of the user's data.
true if it was able to show the UI, false if it failed
bool ShowLoginUI ( const int ControllerIndex, bool bShowOnlineOnly, bool bShowSkipButton, const [FOnLoginUIClosedDelegate](API\Plugins\OnlineSubsystem\Interfaces\FOnLoginUIClosedDelegate) & Delegate )